The history of Mexico encompasses over 13,000 years between the initial migration of indigenous peoples and the modern day. Central and southern Mexico saw the rise and fall of complex indigenous civilizations such as the Olmecs, Mayas and Aztecs. Mesoamerican civilizations developed glyph based writing systems, recording the political history of conquests and rulers. Mesoamerican history prior to European arrival is variously called the pre-hispanic era and the pre-Columbian era. In the 16th Century, the Spanish conquest of the Aztec Empire resulted in the creation of New Spain and the introduction of Christianity. Following Mexico's independence from Spain in 1821, the country faced numerous challenges including conflicts between 'strongmen' or caudillos the Mexican–American War, and the French invasion. In the early 19th century, Mexican Revolution resulted in the rise of the Institutional Revolutionary Party (PRI) which has served as the pre-eminent political party in the country until the modern day. Experiments with nationalization, reforms, and development projects resulted in the Mexican miracle during the 1940s to 1970s. Since then, Mexico has been defined by its incorporation into the North American Free Trade Agreement (NAFTA) in 1994, the Mexican peso crisis, and the Mexican drug war.